Landfill Stability Demonstration
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Landfill Stability Demonstration James River Power Station Utility Waste Landfill Greene County, Missouri for City Utilities of Springfield, Missouri October 16, 2018 Landfill Stability Demonstration James River Power Station Utility Waste Landfill Greene County, Missouri for City Utilities of Springfield, Missouri October 16, 2018 3050 South Delaware Avenue Springfield, Missouri 65804 417.831.9700 TABLE OF CONTENTS 1.0 EXECUTIVE SUMMARY ........................................................................................................................ 1 2.0 INTRODUCTION .................................................................................................................................... 1 3.0 GEOLOGICAL SETTING ......................................................................................................................... 2 3.1 Stratigraphy ..................................................................................................................................... 2 3.1.1 Regional Geologic Setting ..................................................................................................... 2 3.1.2 Bedrock Stratigraphy ............................................................................................................ 2 3.1.3 Local Surficial Geology .......................................................................................................... 3 3.2 Hydrologic Conditions ..................................................................................................................... 3 3.2.1 Regional Hydrology ................................................................................................................ 3 3.2.2 Bedrock Aquifers and Confining Units ................................................................................. 3 3.2.3 Local Hydrology ..................................................................................................................... 4 3.3 Karst Development ......................................................................................................................... 4 4.0 LANDFILL SITING, EXPLORATION AND DESIGN ................................................................................. 4 5.0 LANDFILL OPERATING HISTORY AND PERFORMANCE .................................................................... 5 6.0 POTENTIAL UNSTABLE AREA MECHANISMS .................................................................................... 5 7.0 SITE INVESTIGATION MEANS AND METHODS ................................................................................... 6 8.0 GEOPHYSICAL INVESTIGATIONS ......................................................................................................... 6 8.1 ERT Data .......................................................................................................................................... 7 8.1.2 ERT Data Quality Control ...................................................................................................... 8 8.1.3 Summary of ERT Interpretations .......................................................................................... 9 8.2 MASW Data .................................................................................................................................... 13 8.2.1 MASW Data Quality Control ................................................................................................ 13 8.2.2 Summary of MASW Interpretations .................................................................................... 14 9.0 GEOTECHNICAL INVESTIGATIONS ................................................................................................... 14 10.0 FINDINGS AND CONCLUSIONS ...................................................................................................... 15 11.0 CERTIFICATION ............................................................................................................................... 17 12.0 REFERENCES .................................................................................................................................. 18 LIST OF FIGURES Figure 1. Site Location Map Figure 2. Site Diagram Figure 3. Stratigraphic Column Figure 4. Surface Geology Map Figure 5. JRPS Karst Features Figure 6. JRPS Landfill Development Figure 7. ERT Traverse and MASW Sounding Locations Figure 8. Ground Surface Elevations Figure 9. Top of Rock Elevations Figure 10. Soil and CCR Thickness Figure 11. Interpreted Joint Trend Locations Figure 12. Borehole Location Map October 16, 2018 | Page i File No. 15723-009-00 APPENDICES Appendix A. 3D ERT Profiles Appendix B. MASW Data Appendix C. Borehole Data Appendix D. AE Slope Stability Report Page ii 1.0 EXECUTIVE SUMMARY A Landfill Stability Demonstration was undertaken at the City Utilities of Springfield, MO James River Power Station (JRPS) Utility Waste Landfill (UWL) in accordance with the US Environmental Protection Agency’s (USEPA’s) Coal Combustion Residuals (CCR) Rule, published in the Federal Register on April 17, 2015. The specific requirements for Stability Demonstrations (unstable area demonstrations) are provided in 40 CFR 257.64. The JRPS CCR Landfill is subject to these requirements and is located in a karst area. Karst terrain is one of the considerations to be evaluated in determining whether a CCR landfill is stable. The original JRPS landfill was permitted and developed in 1985 under MDNR permit no. 707704 and is sited in the floodplain of the James River, directly downstream of Lake Springfield. The landfill design incorporated a two-foot thick compacted clay liner and a perimeter embankment for flood protection. The landfill was subsequently expanded laterally and vertically in 1993 under MDNR permit no. 707705, and incorporated a geomembrane liner and storm water detention pond into the design. The JRPS landfill has operated for over 30 years with no evidence of instability. The JRPS landfill stability demonstration involved site reconnaissance to assess karst features; geophysical surveys to determine whether cover collapse sinkholes were forming beneath the landfill; drilling and geotechnical testing to determine engineering properties of the fill material and foundation material; drilling, coring and hydrologic testing around the landfill to characterize stratigraphy, hydrology and karst development; and review of existing stability studies which assessed landfill slope stability. The demonstration found the landfill to be stable. No cover collapse sinkholes were found to be forming within or beneath the landfill. Very few solutional voids were found in the underlying bedrock, and those that were found were generally filled with alluvial sands and gravels. Landfill slopes were found to be stable, both for existing conditions and complete buildout conditions. Total settlement and differential settlement are considered to be insignificant with respect to landfill stability. Sections 8.0 and 9.0 of this report discuss these findings in greater detail. 2.0 INTRODUCTION On April 17, 2015, the United States Environmental Protection Agency’s (USEPA’s) final Coal Combustion Residuals (CCR) Rule was published in the Federal Register. The CCR Rule establishes five (5) location restrictions for CCR landfills. Four (4) of the location restrictions (placement above the uppermost aquifer, wetlands, fault areas, and seismic impact zones) apply only to new CCR landfills. The fifth, unstable areas, applies to both new and existing CCR landfills. Unstable areas are defined as locations that are susceptible to natural or human-induced events or forces capable of impairing the integrity, including structural components of some or all of the CCR unit that are responsible for preventing releases from the unit. Unstable areas can include poor foundation conditions, areas susceptible to mass movement, and karst terrains. 40 CFR 257.64 requires an owner or operator of an existing CCR landfill to demonstrate by October 17, 2018 that recognized and generally accepted good engineering practices have been incorporated into the design of the CCR landfill to ensure that the integrity of the structural components of the CCR landfill will not be disrupted. Section 257.64 further requires the owner or operator to consider all October 16, 2018| Page 1 File No. 15723-009-00 of the following factors, at a minimum, when determining whether an area is unstable: 1) onsite or local soil conditions that may result in significant differential settlement, 2) onsite or local geologic and geomorphological features, and 3) onsite or local human-made features or events (both surface and subsurface). The JRPS UWL is located in an area of karst terrain. This demonstration details the investigations undertaken to assess the stability of the JRPS UWL with respect to site-specific karst features and forms the basis for certification of the UWL’s stability. The location of JRPS is shown in Figure 1. A diagram of the JRPS UWL is provided as Figure 2. 3.0 GEOLOGICAL SETTING 3.1 Stratigraphy 3.1.1 Regional Geologic Setting The JRPS site is located in the Springfield Plateau Sub-province of the Ozark Plateau Physiographic Province. The bedrock surface of the Springfield Plateau generally consists of thick Mississippian-age limestones and cherty limestones above Ordovician- and Cambrian-aged strata. Bedrock generally dips gently toward the west with minor folding and faulting. Most of the area faults have less than 50 feet of displacement. The predominantly limestone